Ingredients, such as thimerosal, formaldehyde, and aluminum, can be harmful in large doses but they are not used in harmful quantities in vaccines.
Children are exposed to more aluminum in breast milk and infant formula than they are exposed to in vaccines.
According to Sanjay Gupta, MD, Chief Medical Correspondent for CNN and practicing neurosurgeon, "you are 100 times more likely to be struck by lightning than to have a serious allergic reaction to the vaccine that protects you against measles." Ellen Clayton, MD, JD, Professor of Pediatrics and Law at Vanderbilt Law School, stated: "The MMR vaccine does not cause autism… And the killed flu vaccine does not cause Bell’s palsy, and it does not trigger episodes of asthma." Herd immunity (or community immunity) means that when a "critical portion" (the percent of people who need to be vaccinated to provide herd immunity) of a population is vaccinated against a contagious disease it is unlikely that an outbreak of the disease will occur so most members of the community will be protected.
Children and adults who cannot be vaccinated due to age, poor health (who are immune-compromised or undergoing chemotherapy, for example), or other reasons rely on herd immunity to prevent contraction of vaccine-preventable diseases. 2019 measles outbreak resulted in the quarantine of over 200 people who had been exposed to the measles on the campuses of the University of California at Los Angeles and California State University.
The CDC reports that pneumonia can be caused by the chickenpox vaccine, and a "small possibility" exists that the flu vaccine could be associated with Guillain-Barré Syndrome, a disorder in which the person’s immune system attacks parts of the peripheral nervous system, in about one or two per million people vaccinated.
Before the rubella vaccine was licensed in 1969, a global rubella (German measles) outbreak caused the deaths of 11,000 babies, and birth defects in 20,000 babies between 19 in the United States.
, which equates to roughly 285 children saved every hour.
The Centers for Disease Control (CDC) estimated that childhood immunization prevented about 419 million illnesses, 26.8 million hospitalizations, and 936,000 early deaths of children born between 19.
They point out that illnesses, including rubella, diphtheria, smallpox, polio, and whooping cough, are now prevented by vaccination and millions of children’s lives are saved.
They contend adverse reactions to vaccines are extremely rare.